e-stop question

Does anyone know where I can find information online about E-stop and where they are required.

The reason I ask is the way I understand you need an e-stop on evry peice of equipment that will stop all moveing items.

We have a bunch of old grinders here that have a stop button for the blade motor and a stop button for the blower motor but no full e-stop for both motors on the same equipmnet.

E-Stops are basically necessary anywhere that active or stored energy can cause harm to someone. The NFPA guidelines are here (WARNING: PDF):
http://www.sti.com/ltr2/access.php?file=pdf/OSHAElecRequirmts_8007.pdf

I always have, and do, consider Emergency Stops to be for PEOPLE safety, and not machine safety. If an E-Stop happens to destroy a machine, but save a life, so be it. The basic intent of an E-Stop is to remove all energy from a system (unless that results in a hazard) and block all motion.

Resetting the Emergency stop should NOT cause any motion at all, anywhere. For that, separate resets and/or starts/enables should be used.

Be careful with what you are doing here!
An e-stop to stop the machine is fine, BUT DO NOT KILL THE POWER TO THE MATERIAL MAGNET!

When the magnet power is killed, the part being held will go flying and hit who knows what. We lost power one time and it wasn't very pretty.

regards,
james

joeparrish said:

Does anyone know where I can find information online about E-stop and where they are required.

Click to expand...

Try: http://www.hs-compliance.com/uploaded/documents/THE EMERGENCY STOP.pdf

and: http://machinerysafety101.com/2009/03/06/emergency-stop-whats-so-confusing-about-that/

you can then carry on regardless!

OSHA Regulations are not a great help when it comes to E- Stops, most of what OSHA has to say is covered in 1910 Subpart S. OSHA does make reference to 1971 National Electrical Code in the mandatory appendix, and has proposed a rule change (Electrical Standard; Proposed Rule – 69:17773-17842) to bring that in line with the current NFPA 79 2007 , The Electrical Standard for Industrial Machinery. This standard is very much the same as ISO 13850:2006 The International Organization for Standards Safety of machinery — Emergency stop — Principles for design.
In short, there are three types of stop circuits:

• Category 0: Stopping by immediate removal of power to the machine actuators (i.e.,uncontrolled)
• Category 1: A controlled stop with power to the machine actuators available to achieve the stop and then removal of the power when the stop is achieved
• Category 2: A controlled stop with power left available to the machine actuators

The category you use should be determined by the risk assessment.
The function of the Emergency stop shall be to “Avert a rising or reduce existing hazards to persons, machinery or work in progress, and Be initiated by a single human action when the normal stopping function is inadequate for this purpose” (ISO 13850:2006).
Under NFPA 79 2007, it:

• Shall override all other functions and operations in all modes, and
• Power to the machine actuators that can cause a hazardous condition shall be removed as quickly as possible without creating other hazards (e.g., by the provisions of mechanical means of stopping requiring no external power)
• Reset shall not initiate a restart

NFPA 79 2007 and ISO 13850:2006 are identical in the requirements that Actuators of emergency stop devices shall be colored RED. The background immediately around pushbuttons and disconnect switch actuators used as E-Stop devices shall be colored YELLOW. The actuator of a pushbutton-operated device shall be of the palm or mushroom-head type. Emergency stop devices shall be located at each operator control station and at other locations where emergency stop is required. They shall be positioned for easy access and for non-hazardous operation by the operator and others who may need to operate them. Measures against inadvertent operation should not impair accessibility. Any action on an actuator resulting in an emergency stop command shall also result in the latching-in of the control device…the emergency stop command must be maintained until the control device is reset.
It is also important to remember that the emergency stop function shall not be applied for use as a substitute for safeguarding measures and other safety-critical functions, but should be designed for use as a backup measure.
You should also remember to give consideration to the operating conditions, Components used to achieve the emergency stop, shall be capable of operating correctly under the expected operating conditions and environment. Some things to think about are:

• Frequency of operation and the need for periodic testing in the case of infrequent operation, and
• Vibration, shock, temperature, dust, foreign bodies, moisture, corrosive materials, fluids, etc.

Other types of Emergency Stop devices include (but are not limited to): Pull-cord-operated switches; and Push–bar-operated switches.
It is also important that your Emergency Stop clearly indicates what machine it controls if it is not obvious from its location.
You may also want to check your local electrical code, as it may impose additional requirements on you for your Emergency Stop circuits.
Emergency Stop controls are very important and must be in conformity with all appropriate codes, in the U.S. That means NFPA 79 2007.

E-Stop Requirements

First, Thanks to Silva Foxx for posting a link to my blog, Machinery Safety 101! I really appreciate it!

Getting to the question at hand, I have a couple of comments:

1) Emergency Stops are considered to be complementary protective measures. They are not safeguarding devices. Their intent is to help a user to limit the harm that may be occurring, but they are not preventative devices.

2) There is generally NO requirement for a machine to have an emergency stop. Not all machines can benefit from having an e-stop system, and so therefore requiring one on every machine is counterproductive. A risk assessment is required to determine the need for an e-stop, and the degree of reliability required, in addition to reading the relevant product safety standard which MAY require an emergency stop.

In relation to the original question regarding grinders and retrofitting them with e-stops, go first to your local regulations (State or Provincial OHS regulations), then go to your National regulations (If any. OSHA in the USA.), then go to the voluntary technical standards (in this case, ANSI B11.9, Grinding Machines - Safety requirements for construction, care and use).

The general requirement for location is 'within easy reach' of the normal operator location, so if the operator normally stands in front of the grinder, then this is the normal location. Keep in mind that you don't want to place the e-stop device so the operator would have to reach over the hazard. This is generally not permitted in most jurisdictions.

Check out machinerysafety101.com for more on emergency stops.

Not trying to thread pirate but can you tell me about the risk assesment that is done? Is this a standard checklist/form?

Risk assessment

Risk assessment is a process, not a form, although forms can be used as tools within the process.

The process goes generally like this:

Stage 1
Hazard Identification & Evaluation (what can do harm & how much)
Risk Estimation (scoring)
Risk Evaluation (is it safe enough?)

Stage 2
Risk Mitigation (apply the Hierarchy of Controls)

Stage 3
Risk Estimation (scoring)
Risk Evaluation (is it safe enough?)

You keep looping through until the risk is reduced enough to meet regulatory requirements as a minimum.

ISO 14121-1 and -2 lay out the risk assessment process. You can also find some information in ANSI B11 General Safety Requirement (just published this year).

A great text on the subject is Bruce Main's "Risk Assessment: Basics and Benchmarks".

I use CIRSMA risk assessment software in my practice, and I can provide you a quotation if you are interested. My corporate web site is http://www.complianceinsight.ca.

Email me offline if you want to discuss this in more detail!

DougNix,

Thank you for the very informative reply. I'm only in the learning process right now so the book should be a good start for me.

Thanks

Risk Assessment: Basics and Benchmarks

Here's where to buy a copy of Bruce Main's book:

http://www.designsafe.com/products.php#books

He includes a copy of his own risk assessment software with the book, but I am not a fan of the software. CIRSMA is by far a better product.

See http://www.industrialsafetyintegration.com for more on CIRSMA.

must the legend plate be yellow in the states? I have a coworker that insists that is only a european thing.

Your co-worker is wrong.

Industrial electrical panel design in the USA is governed by ANSI/NFPA 79. Here's the clause from the 2007 edition of the standard:

10.2.2.3 Emergency Stop. RED shall be used for emergency stop actuators in accordance with 10.7.3.

10.7.3 Emergency Stop Actuators. Actuators of emergency stop devices shall be colored RED. The background immediately around push buttons and disconnect switch actuators used as emergency stop devices shall be colored YELLOW. The actuator of a push button-operated device shall be of the palm or mushroom-head type and shall effect an emergency stop when depressed. The RED/YELLOW color combination shall be reserved exclusively for emergency stop applications.

Exception: The RED/YELLOW color combination shall be permitted for emergency stop actuators in accordance with 10.8.4.

10.8.4 Actuators.
10.8.4.1 Actuators of emergency switching off devices shall be colored RED. The background immediately around the device actuator shall be permitted to be colored YELLOW.

10.8.4.2* Where the emergency switching off initiating device is separate from the emergency stop device, the emergency switching off initiating device shall be functionally identified.

There you have it. RED and YELLOW combination is REQUIRED.

You may want to point your co-worker to this article:
http://machinerysafety101.com/2009/03/06/emergency-stop-whats-so-confusing-about-that/

Some thoughts on E stops based on my electrical experience with them and 20 years in Safety field.

!. They are good things - properly applied and properly used.
2. The most common mistakes I see with them is substituting them for on off controls AND restarting machine just by reset of E stop (very very common). I favor a lockout relay that can only be reset by supervisor (key switch) or maintenance. I think this should be mandatory especially so in the case of machines with multiple E stops and triply so where E stops are on backside of machine.
3. Cutler Hammer is the type I am most familiar with. They use a normal type NC contact block. The problem I found is with the block completely disconnected from operator the circut is still made. THe only solution (and not a complete one and poor compromise) is I use two contacts in series. I have started to do this with all STOP switches and I use LOctite on the screws to prevent them from falling away from actuator.
4. Dont need lockout and tagout with E stop. No and TRIPLE no. In my mind the only time I do not need LOTO is on cord connected and I have the plug in MY lap.

5 If E stop is good on a machine then it must be good on all. BALONEY.
There is no need for an E stop on a pedestal grinder (UNLESS it has a braking function). I would be inclined to put a big red STOP button on the stop switch though. In the case of the grinder with a fan on it I would run both off one disconnect, fuse or put in breaker w/ overload for both and run both off one start stop. Simple clean and you avoid multiple power supply issues in interlock circuits.

There are cases where an E stop CANNOT completely shut down a machine ie the magnet mentioned prevously (magnets used for lifing or as chucks MUST stay energized lest you drop steel on someone or watch a flywheel go into orbit from a lathe. Also goes for vacuum lifting gear and chucks. This is just this one example I do NOT advocate a checklist
"we filled out the checklist and it did not include a magnet so it must not have been important" - Joe's funeral is next week.

I would put one or two brains together and evaluate a machine to answer teh question "how can we mangle someone with this". Not one person can know it all and it is too easy to not think of something. I have learned this lesson the hard way in Safety and it is all too easy to do - I have done it - thankfully on small stuff.

Get someone who really knows the machine and process. Really experienced operators and maintenance mechanics are often a great resource. Older machines can be tough to do and hard to retrofit have no doubt about it.

OSHA and your state program have consultants. Some of these guys are pretty sharp BUT remember they are pretty much oriented to the regulations.

In the past I looked at Allen Bradley articles thought they were pretty good.

Dan Bentler

Thank you DougNix!

E- stop button should bs wired to a safety relay as category 4, 3 or 2 says, i dont know if you heared about that or not